Do you need a professional lens?
What exactly does the extra money buy you?
It is often said that investing in a good lens for your camera is a better option for improving image quality than upgrading your dSLR body. There is a lot of truth in this, since without the use of quality glass the full potential of the imaging sensor cannot be realised. Regardless of how many pixels the camera has, or how advanced the processor and analogue to digital conversion components are, the light has to first pass through and be focussed by the elements of the optic in use. It is no secret that budget or bundled ‘kit’ lenses produce images with lower sharpness and lack some of the advanced features of professional models and in the pro arena this can become very evident.
However, as is the case with camera bodies, the person buying a product should ask themselves whether or not they really require those features and if the additional image quality will be noticeable at the sizes they frequently print images. As lens technology grows more advanced, the jargon new models spawn becomes increasingly more complex and convoluted, leaving potential users feeling a little overwhelmed and unsure how each aspect is supposed to help their photography. In this article we break down the common features found in top-level lenses and why you would want to part with your cash for them.
Construction and weather-sealing is a main aspect of pro-spec lenses in which working photographers may invest. For making images in adverse weather conditions, or in tough environments, having a well-built lens is as important as a solid camera body. Pro bodies are often built using a predominance of metal, such as magnesium alloy, which is capable of withstanding even the most demanding conditions. It makes very little sense to spend money on a tough camera if the lens attached to it is not up to the job. The main manufacturer’s pro lens ranges are designed specifically to integrate and be paired with their high-end cameras, sharing construction materials and weight balance. Furthermore, the actual shape and profile are often tailored to ensure ultimate weather sealing – the lens bayonet threads and camera mount plates interlock to keep out dirt and moisture.
Kit lenses have a less complex optical design to keep down production costs. One trade-off from this is a lack of full time manual focus, which requires the lens elements to be movable, whether or not the autofocus system is active. This design is coupled with a higher-spec focussing motor, which contributes to the greater cost of the lens. Attempting to move the elements of a budget lens, with AF enabled, can damage the moving parts within the lens barrel. Having the ability to manually refine focus at any time is a huge advantage – modern AF systems are incredibly accurate, but if the photographer has to recompose slightly, it may be necessary to nudge the plane-of-focus to compensate. Having to turn AF off and then on again can waste precious time and result in potentially missed shots.
Aspherical lens elements
Aspherical lenses (often denoted by Asph on the lens barrel) help overcome the deficiencies of standard spherical glass in the formation of a uniformly sharp image. The elements inside a lens are ground to highly precise curvatures, which are calculated as part of a sphere – the angle of the lens surface would eventually form a spherical shape. This is necessary to correctly focus an image, by refracting the light as it passes through the glass, however the design is incapable of perfectly converging light rays, thereby producing photos that are less than perfectly sharp (spherical aberration). Aspheric lenses are not deigned around a spherical model and have (rather unsurprisingly) shapes which are not part of a perfect sphere. This redirects light to converge more effectively at the focussed point (the sensor), yielding a sharper image across the frame. The manufacturing process is more complex, which makes lenses featuring these elements more expensive, but along with other engineering techniques, helps produce better quality shots.
Extra-Low Dispersion and Fluorite lenses are precision-manufactured to reduce the impact of Chromatic Aberrations in images. CA (coloured banding around high contrast edges in a shot) is caused by unequal convergence of different wavelengths of light at the focal plane. While it can be reduced fairly effectively in software, it is better to have the effect corrected before the image is made and special glass elements are a solution. Fluorite glass has a low refractive index, which means the path of the light passing through it is not altered (refracted) as much as in other optical materials. This means that glass coated with fluorite is more able to focus all colours at the same plane, thereby minimising chromatic aberration. Meanwhile ED or ULD (Ultra-Low Dispersion) elements are coated with other substances that minimise refraction, further reducing the appearance of CA. Pro-spec optics feature a greater proportion of ED to non-ED lens elements, which explains their superior colour rendition, contrast and overall refractive performance. Many of the chemicals and compounds used to coat the glass at the manufacturing stage do not exist in great abundance in nature (as is the case with fluorite) meaning these must be synthesised artificially, forcing up production costs. Well worth the investment over the long-term.
Along with internal focussing often comes a focus distance scale on high-end lens models. This can be used to accurately calculate focussing distance (using the hyperfocal distance method) or to focus when shooting ‘from-the-hip’. While not an essential feature, it is useful in many cases, where relying of AF is not a viable option, such as in extreme low-light conditions.
When using a camera with an advanced AF system, it makes sense to use a lens which is able to keep up with and compliment that functionality. Having AF modes specifically tailored to your shooting situation will help predict how best to capture an image. Many pro lenses have an extra AF-On button for locking focus – essential for holding focus once you have achieved it in fast-paced conditions.
Another handy extra, the tripod collar found on many heavy zoom and prime lenses can be used to quickly attach your camera set-up to a tripod for a balanced system and to rapidly rotate between landscape and portrait orientations. This is another aspect which helps the working photographer capture fleeting images in demanding shooting arenas.